With reference to FIGS. 8 and 9, two examples are given to describe operations in a mobile communication system of the LTE (long term evolution) scheme specified by the 3GPP at a time when a mobile station UE having a connection #1 established with a radio base station eNB detects an RLF (radio link failure).
First, a first example is described with reference to FIG. 8. As shown in FIG. 8, in a state where a connection including a SRB (signalling radio bearer) and a DRB (data radio bearer) is established between the mobile station UE and the radio base station eNB, the radio base station eNB transmits an “RRC Connection Reconfiguration (connection reconfiguration signal)” including a release request of a DRB #15 to the mobile station UE in Step S3001.
In Step S3002, the mobile station UE performs releasing processing of the DRB #15 in response to the “RRC Connection Reconfiguration”, and then transmits an “RRC Connection Reconfiguration Complete (connection reconfiguration completion signal)” to the radio base station eNB, so as to notify that the releasing processing of the DRB #15 is completed.
Thereafter, the mobile station UE detects an RLF before the “RRC Connection Reconfiguration Complete” reaches the radio base station eNB, and transmits an “RRC Connection Re-establishment Request (connection re-establishment request signal)” to the radio base station eNB in Step S3003.
In Step S3004, the radio base station eNB transmits an “RRC Connection Re-establishment (connection re-establishment signal)” to the mobile station UE. In Step S3005, the mobile station UE transmits an “RRC Connection Re-establishment Complete (connection re-establishment completion signal)” to the radio base station eNB. As a result, the connection (SRB1) is re-established between the radio base station eNB and the mobile station UE.
Subsequently, in Step S3006, the radio base station eNB transmits an “RRC Connection Reconfiguration (connection reconfiguration signal)” to the mobile station UE. As a result, a connection (SRB2 and DRB) is re-established between the radio base station eNB and the mobile station UE.
Next, a second example is described with reference to FIG. 9. As shown in FIG. 9, in a state where a connection including an SRB and a DRB is established between the mobile station UE and the radio base station eNB, the mobile station UE detects an RLF in Step S4001, and then the radio base station eNB transmits an “RRC Connection Reconfiguration” including an addition request of a DRB #15 to the mobile station UE in Step S4002.
In such a case, the mobile station UE transmits an “RRC Connection Re-establishment Request” to the radio base station eNB in Step S4003 without performing adding processing of the DRB #15.
In Step S4004, the radio base station eNB transmits an “RRC Connection Re-establishment” to the mobile station UE. In Step S4005, the mobile station UE transmits an “RRC Connection Re-establishment Complete” to the radio base station eNB. As a result, the connection (SRB1) is re-established between the radio base station eNB and the mobile station UE.
Subsequently, in Step S4006, the radio base station eNB transmits an “RRC Connection Reconfiguration” to the mobile station UE. As a result, a connection (SRB2 and DRB) is re-established between the radio base station eNB and the mobile station UE.